Cannot copy Mplayer audio files to my Sansa c250. Why?

For at least 5-6 years I have has no problems copying Mplayer audio files from my PC to my Sansa c250.

Now, suddenly, I am getting this error message (typical):

"Copy File

Cannot copy 594  My Summer Self

This device has either stopped responding or has been disconnected. Although this device supports audio files, it does nor support .mp3 files. If possible, use a media program that can convert the file before copying it. "

I’m already using the intermediate step that asks if I want the file to converted and copied so it will play on my device.

What might be my problem ?

Using Sansa Support online,  I installed “firmware update” even though it was the same number as my original version.

Now I can download a MPlayer audio file to my Sansa c250 (good), except it downloads it nine times (bad) !

What the heck is going on?

Not familiar with Mplayer audio files so can’t help. Is this a media “management” player similar to Windows Media Player, Media Monkey, etc.? If so, why not simply drag & drop (copy & paste) using Windows Explorer and avoid the “management” software altogether?